Inkjet Printing
Nowadays a lot of printed matter is produced carrying a reproduction of a colour image. A large part of these colour prints are produced using offset printing but in office and home environments a lot of colour prints are made using relatively small printing apparatuses.
One of the possible printers used is an inkjet printer. In an inkjet printer drops of ink are jetted out of nozzle toward a receiving layer which may be e.g. specially coated paper. Usually an inkjet print head has an array of nozzles, each nozzle jetting ink to different locations at the same time. The ink jetted out of the nozzles by use of, e.g. thermal or piezoelectric actuators, creating a pressure wave. It is normally the intention that the size of the droplets can be kept constant or that there is a good control of the droplet size in ink jet printers capable of recording variable droplet sizes.
Shuttling Print Head with Header Tank
Inkjet printing technology is also used in large format, high volume printers in more industrial applications. Inkjet print heads can be as large as the transversal size of an image or text to be printed but usually the size of the print head is smaller. Page wide print heads are still expensive and less reliable than smaller types.
An inkjet printer prints an image when a receiving sheet, e.g. a sheet of paper, is transported in one direction and passed gradually underneath a printing station of the printer. A print head which has a size smaller than the receiving sheet shuttles transversal over the receiving sheet and consecutively records one or more lines when shutting over the sheet paper. The image is composed gradually. It is possible that several print heads are used to record different colours and a colour image is recorded by superposition of the different colour images.
Small printers usually have a small cartridge, optionally with integrated print head nozzles, containing only a limited amount of ink. When empty these cartridges have to be replaced. In order to enable continuous operation of a print head, an ink tank containing an ink supply can be coupled to the print head.
High end inkjet printers in industrial applications having a high throughput or large formats consume a large amount of ink. The inkjet print head of a high end printer is coupled to an ink tank mounted on the shuttling carriage carrying the print head. This ink tank is called a header tank and can be refilled out of a large capacity ink tank or cartridge which is stationary in the apparatus.
It is possible that a fixed large capacity ink tank is provided but usually the header tank is coupled to an exchangeable ink cartridge which acts as a main supply. This has the advantage that it is easier to change the type of ink used in an inkjet printer. By replacing the ink cartridge the printer can be quickly converted to print with an another colour or type of ink. When using a fixed large capacity ink tank this is more difficult.
As mentioned above most systems use a header tank close to the inkjet printhead to supply the ink to the inkjet printhead, but it is also possible that the printhead is directly coupled to the ink cartridge or main ink tank of the printer.
The ink cartridge used has to be connected to the ink supply system of the inkjet printer. Even when the printer has a fixed large capacity ink tank, the tank has to be refilled using an ink cartridge.
Hitherto different systems have been used. In US 2002/180 848, herein incorporated by reference in its entirety for background information only, a self-sealing plug is pierced by a needle like hollow instrument. When separating the plug reseals itself after the needle is retracted.
In EP 1 277 584, herein incorporated by reference in its entirety for background information only, a joint pipe opens a valve in the valve mechanism of the ink container. Leakage from the opening of the inkjet printer is avoided by capillary forces of the small needle-like opening.
Coupling systems do exist wherein the needle having a lateral opening at the end is covered by a sliding sealing element. When retracting the cassette a rubber sheath slides upward to cover the opening in the side of the needle. This avoids evaporation of ink at the opening which could block the opening. This system however has certain drawbacks as noted below.                The sealing of the opening in the needle is relatively low. The rubber sheath has to slide over the needle so the radial pressure exerted on the wall of the needle is rather low to enable the sliding of the sheath. Therefore ink can still escape when pressure builds up inside the printer. The pressure of the ink can push back the rubber which exerts only minimal pressure as only the elasticity of the rubber ensures a pressing force. Minimal pressure of the ink will cause leakage.        By sliding the rubber sheath over the opening of the needle the inner wall of the sheath can be damaged by sliding over the opening in the needle. The inner layer of material of the rubber sheath protrudes inside the hole of the needle due to the radial pressing force and is chamfered by edge of the hole at the needle edge. This abrasion can cause the sealing to be defective after a certain time.        A small amount of ink can be trapped between the sealing of the cartridge and the rubber sheath causing contamination of the coupling system and giving problems due to dried ink, etc.        
An important drawback of all these coupling systems is that the ink flow rate is rather restricted due to the small diameter of the needle-like structures. The small opening causes a considerable pressure drop over the coupling, thus limiting the possible ink flow. This can be counteracted by applying a positive pressure on the outside of the ink container inside the ink cartridge.
In US 2001/12 038, herein incorporated by reference in its entirety for background information only, the connection is established using a compressive seal and a needle displacing the sealing ball while the ink bladder inside the cartridge is pressurized at the outside.
US 2002/0001009, herein incorporated by reference in its entirety for background information only, discloses an ink container slidably mounted on an ink supply station. The container has a collapsible ink reservoir in a pressurized chamber.
A drawback of the above-mentioned systems is that the opening of the printer to the ink cartridge is not closed off when no cartridge is attached so ink leakage is possible under certain conditions, e.g. due to pressure changes inside the printer. Some systems rely on the negative pressure inside the ink supply system in the printer to avoid leakage. This can however not be relied upon at all times.
Also when ink cartridges are pressurized the likelihood of leakage from a stored cartridge is greater than that of non-pressurized cartridges. Pressurized cartridges also demand higher fabrication standard to provide an air-tight housing. This makes them more expensive. Accidentally puncturing the outer shell of such cartridges also makes them inoperable.
Valve units of ink cartridges need to have a higher quality when pressure is maintained in a stored cartridge. This is undesirable as it makes the cartridges more expensive.
In U.S. Pat. No. 5,963,238, herein incorporated by reference in its entirety for background information only, a double valve system is used but as the connection is made a large quantity of air is included in the ink stream causing possible problems due to air bubbles. Also ink left at the outside of the coupling elements can dry and block the valve system in further use.
In U.S. Pat. No. 6,550,899, herein incorporated by reference in its entirety for background information only, the same problem exists, air is enclosed and when the valve pair is de-coupled ink is left at the outside giving possible problems due to drying.
In US 2003/202060, herein incorporated by reference in its entirety for background information only, a combination of a needle-like coupling element and a compressive seal cause problems after frequent use of the coupling system.
It is clear there is a need for a system for coupling an ink cartridge to an inkjet printer ensuring absolutely no leakage from the cartridge or printer and having a high cross-section allowing a high ink flow without the need for pressure assisted ink flow. Also problems inherent to sealing sliding over an opening need to be avoided.